Dielectric sidewall structure for quality improvement in ge and sige devices

ABSTRACT

Some embodiments relate to an integrated circuit (IC) disposed on a silicon substrate, which includes a well region having a first conductivity type. An epitaxial pillar of SiGe or Ge extends upward from the well region. The epitaxial pillar includes a lower epitaxial region having the first conductivity type and an upper epitaxial region having a second conductivity type, which is opposite the first conductivity type. A dielectric layer is arranged over an upper surface of the substrate and is disposed around the lower epitaxial region to extend over outer edges of the well region. The dielectric layer has inner sidewalls that contact outer sidewalls of the epitaxial pillar. A dielectric sidewall structure has a bottom surface that rests on an upper surface of the dielectric layer and has inner sidewalls that extend continuously from the upper surface of the dielectric layer to a top surface of the epitaxial pillar.

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.17/148,657, filed on Jan. 14, 2021, which is a Continuation of U.S.application Ser. No. 16/145,585, filed on Sep. 28, 2018 (now U.S. Pat.No. 10,896,985, issued on Jan. 19, 2021), which is a Divisional of U.S.application Ser. No. 15/273,880, filed on Sep. 23, 2016 (now U.S. Pat.No. 10,147,829, issued on Dec. 4, 2018). The contents of theabove-referenced patent applications are hereby incorporated byreference in their entirety.

BACKGROUND

Semiconductor devices based on silicon, such as transistors andphotodiodes, have been widely used for the past three decades. In recentyears, semiconductor devices based on alternative materials, such asgermanium, are becoming more widely used because they can offeradvantages over silicon-based semiconductor devices. For example, puregermanium (Ge) as well as its silicon alloys (hereinafter “SiGe”), whichexhibit a molar ratio of silicon to germanium according toSi_(1-x)Ge_(x), may be advantageous in the area of photodetectors,because their bandgaps are more adjustable than those of silicon-onlymaterials. This allows SiGe devices to more efficiently capture photonsand makes SiGe devices attractive in the area of photodetectors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of asemiconductor structure having an epitaxial pillar, which includes a pnjunction photodetector, with a dielectric sidewall structure alongsidewalls of the epitaxial pillar.

FIG. 2 illustrates a top view of FIG. 1 's semiconductor structure takenalong the cross-sectional line as shown in FIG. 1 .

FIG. 3 illustrates a top view of FIG. 1 's semiconductor structure takenalong the cross-sectional line as shown in FIG. 1 .

FIG. 4 illustrates a cross-sectional view of some embodiments of asemiconductor structure having an epitaxial pillar, which includes a pinjunction photodetector, with a dielectric sidewall structure alongsidewalls of the epitaxial pillar.

FIG. 5 illustrates a cross-sectional view of some embodiments of asemiconductor structure having an epitaxial pillar, which includes aphotodetector, with a dielectric sidewall structure having rounded uppercorners.

FIG. 6 illustrates a cross-sectional view of some embodiments of asemiconductor structure having an epitaxial pillar, which includes aphotodetector, with a dielectric sidewall structure having rounded uppercorners.

FIGS. 7-19 illustrate a series of cross-sectional views of someembodiments of a semiconductor structure at various stages ofmanufacture.

FIG. 20 illustrates a flowchart of some embodiments of a method formanufacturing a semiconductor structure consistent with some examples ofFIGS. 7-19 .

FIGS. 21-24 illustrate a series of cross-sectional views of someembodiments of a semiconductor structure at various stages ofmanufacture.

FIG. 25 illustrates a flowchart of some embodiments of a method formanufacturing a semiconductor structure consistent with some examples ofFIGS. 21-24 .

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Photodetectors, such as photodiodes, are used in a variety of electronicdevices, such as digital cameras, smart phones, and optical sensors,among others. High-quality photodetectors often include a region ofepitaxially-grown semiconductor material disposed over a semiconductorsubstrate. To form the epitaxially-grown semiconductor material, aresist protective oxide (RPO) layer is formed over an upper surface ofthe semiconductor substrate, a silicon nitride layer is formed over theRPO layer, and a dielectric layer, such as un-doped silicate glass(USG), is formed over the silicon nitride layer. In some conventionalapproaches, a plasma etch is then carried out with a mask in place toform a recess through each of the dielectric layer, silicon nitridelayer, and RPO layer, thereby exposing an upper surface of thesemiconductor substrate. The semiconductor material corresponding to aphotodetector is grown in the recess. However, the present disclosureappreciates that physical bombardment of ions in the plasma etch candamage the exposed upper surface of the semiconductor substrate, forexample by causing small fractures or dislocations, and can thus changethe previously monocrystalline structure of the semiconductor substrateto a polycrystalline lattice structure. When the epitaxially-grownsemiconductor material is formed on this damaged region of thesemiconductor substrate to establish the photodetector, the resultantdevice may suffer from undesirable leakage due to the underlyingfractures/dislocations.

Other conventional approaches terminate the plasma etch after a recesshas been partially formed but before the upper surface of thesemiconductor substrate is exposed, and then use a wet etch to removethe final portion of the RPO layer to expose the upper surface of thesemiconductor substrate. While this alternative approach can avoid orlimit plasma damage to the upper substrate surface, aspects of thisdisclosure appreciate that using this wet etch to remove the RPO layercan “undercut” the silicon nitride layer. When the semiconductormaterial corresponding to a photodetector is grown with this “undercut”in place, the “undercut” can lead fill issues in which the semiconductormaterial does not completely fill outermost portions of the recess underouter edges of the silicon nitride layer. Thus, this wet etch approachcan also lead to less than optimal device characteristics.

The present disclosure provides devices and methods that improve devicecharacteristics of photodiodes over conventional approaches. Inparticular, some embodiments of the present disclosure providesemiconductor devices that include a pillar of epitaxial semiconductormaterial that corresponds to a photodiode. This pillar of semiconductormaterial contacts an upper surface of the underlying semiconductorsubstrate with little or no plasma damage, and is surrounded by adielectric sidewall structure that is configured to prevent and/orsignificantly limit “undercut” during manufacture of the device. Thus,the semiconductor devices disclosed can provide better devicecharacteristics than conventional approaches in some regards.

FIG. 1 illustrates a cross-sectional view of an integrated circuit (IC)100 in accordance with some embodiments; while FIGS. 2-3 , which are nowdescribed in concurrently with FIG. 1 as shown by the cross-sectionallines in FIGS. 1-3 , illustrate top views of the FIG. 1 's IC 100 atvarious depths. The IC 100 includes a substrate 102 including a wellregion 104 having a first conductivity type (e.g., n-type) which islaterally surrounded by an isolation region 106. In some embodiments,the substrate 102 is a monocrystalline silicon substrate or asilicon-on-insulator (SOI) substrate, and the isolation region 106 is awell region having a second conductivity type (e.g., p-type) oppositethe first conductivity type. A dielectric layer 108, which can manifestas an RPO layer in some embodiments, is arranged over an upper surfaceof the substrate 102. The dielectric layer 108 extends over outer edgesof the well region 104 and covers isolation region 106, and includes anopening that leaves an inner portion of the well region 104 exposed. Asilicon nitride layer 110 is disposed over the dielectric layer 108, anda low-κ dielectric layer 112 is disposed over the silicon nitride layer110. An epitaxial pillar 114, which is made of pure Ge or a SiGe alloyhaving a monocrystalline lattice, extends upward from the inner portionof the well region 104 and through the opening in the dielectric layer108.

The epitaxial pillar 114 includes a lower epitaxial region 114 a havingthe first conductivity type and an upper epitaxial region 114 b havingthe second conductivity type. The upper and lower epitaxial regions 114a, 114 b meet at a junction 115 to establish a photodiode. When animpingent photon 116 of sufficient energy strikes the photodiode, anelectron-hole pair is created, and the carriers of the pair are sweptacross the junction 115 by a built-in electric field within thephotodiode. Thus, when the IC 100 is exposed to photons 116 ofsufficient energy, a photocurrent is produced in which holes move towardan anode of the device (for example from junction 115, through lowerepitaxial region 114 a, through well region 104, through highly dopedwell contact region 118, up lower contact 120, and through firstconductive line 122), and in which electrons move toward a cathode ofthe device (for example, from junction 115, though upper epitaxialregion 114 b, through upper contact 124, and through second conductiveline 126). In some embodiments, the first and second conductive lines122, 126 are aluminum copper interconnect lines disposed over thesubstrate 102, and are arranged to include a window opening 128 alignedover an upper surface of the epitaxial pillar 114 and through which theincident photons 116 may pass to reach the epitaxial pillar 114 and itscorresponding photodiode. An anti-reflective coating (ARC) 130, such asa silicon nitride coating, is disposed over the first and secondconductive lines 122, 126 and lines the sidewalls and lower surface ofwindow opening 128.

Notably, a dielectric sidewall structure 132 laterally surrounds theepitaxial pillar 114 and has a bottom surface that rests on an uppersurface of the dielectric layer 108, such that the dielectric sidewallstructure 132 and dielectric layer 108 collectively line the full heightof sidewalls of the epitaxial pillar 114. In some embodiments, thedielectric layer 108 and dielectric sidewall structure 132 have the samedielectric material composition as one another. For example, in someembodiments the dielectric layer 108 and dielectric sidewall structure132 are both made of silicon dioxide (SiO₂) and can have equal etchingrates for a predetermined etch. In other embodiments, the dielectriclayer 108 and dielectric sidewall structure 132 are made of materialsthat exhibit slightly different etch rates, for example, but which arewithin 35% of one another, within 10% of one another, or even within 5%of one another for a predetermined etch. Thus, the dielectric layer 108can have a first etch rate and the dielectric sidewall structure 132 canhave a second, slightly different etch rate, wherein the first etch ratecan be between 70% and 130% of the second etch rate in some embodiments,or even between 95% and 105% of the second etch rate in otherembodiments. For example, in some other embodiments, dielectric layer108 and/or dielectric sidewall structure 132 can be made of siliconnitride Si₃N₄, and can be formed by plasma enhanced chemical vapordeposition (PECVD) or can be thermally grown.

As will be appreciated further herein, during manufacturing, thedielectric sidewall structure 132 helps limit etching damage to theupper surface of the well region 104 and, because the etching rates ofthe dielectric layer 108 and dielectric sidewall structure 132 are thesame or similar, helps prevent the dielectric layer 108 fromundercutting the silicon nitride layer 110. In this way, the epitaxialpillar 114 can be formed with outer sidewalls that are planar orsubstantially planar, and which are vertical or substantially verticalto facilitate good filling by epitaxial growth without gaps or voids.Although the epitaxial pillar 114 and dielectric sidewall structure 132are illustrated as being square or rectangular as viewed from above, itwill be appreciated that in other embodiments the epitaxial pillar 114and dielectric sidewall structure 132 can be circular, oval, orpolygonal in shape as viewed from above, and/or can have square cornersor rounded corners as viewed from above. Further, although FIG. 1illustrates an example where the lower epitaxial region 114 a is n-typeand the upper epitaxial region 114 b is p-type, in other embodiments thelower epitaxial region 114 a can be p-type and the upper epitaxialregion 114 b can be n-type, provided the conductivity types of the otherregions is correspondingly transposed.

The dielectric sidewall structure 132 has innermost sidewalls that arealigned with innermost sidewalls of the dielectric layer 108. Thedielectric sidewall structure 132 also separates an inner sidewall ofthe silicon nitride layer 110 from an outer sidewall of the epitaxialpillar 114, which helps limit or prevent undercut of the silicon nitridelayer 110. A lower surface of the dielectric sidewall structure 132 isco-planar with a lower surface of the silicon nitride layer 110 in someembodiments, and an upper surface of the low-κ dielectric layer 112 isco-planar with both an upper surface of the dielectric sidewallstructure 132 and an upper surface of the epitaxial pillar 114 in someembodiments. In some embodiments, the dielectric layer 108 acts as anRPO layer, which is a silicide-blocking layer to maintain a resistivityof the underlying silicon substrate and/or to maintain a resistivity ofa polysilicon layer over the underlying silicon substrate. For example,if the IC 100 includes a polysilicon resistor, the RPO layer can bepatterned to remain in place over the polysilicon resistor and alsooverlie regions of the substrate 102. Thus, when silicide is formed overother regions of the IC, such as on source/drain regions and/or gateelectrodes for example to form ohmic contacts, the RPO layer is left inplace over the polysilicon resistor to prevent the silicide fromcontacting the polysilicon resistor, and thereby maintaining theresistance of the polysilicon resistor.

FIG. 4 shows a cross-sectional view of some embodiments, wherein theepitaxial pillar 114 further comprises an intrinsic region of pure Ge oran intrinsic region of SiGe alloy separating the lower epitaxial region114 a from the upper epitaxial region 114 b. Thus, in FIG. 4 , thephotodiode includes a lower epitaxial region 114 a that is n-type, anintermediate region 115′ that is intrinsic Ge or SiGe, and an upperepitaxial region 114 b that is p-type; although the p-type and n-typedoping could be transposed in other embodiments. In FIG. 4 , a lowermostportion of the intrinsic region 115′ has a first height, as measuredfrom an upper surface of the substrate 102, and a lowermost portion ofthe silicon nitride layer 110 has a second height that is less than thefirst height, although the thickness of the lower epitaxial region 114 acould be altered in other embodiments to change the first height to begreater than that of the silicon nitride layer 110.

FIG. 5 shows a cross-sectional view of some embodiments, wherein innersidewalls of the dielectric sidewall structure 132 have rounded uppersurfaces 140, and where an upper surface of the epitaxial pillar 114flares outward over the rounded upper surfaces. Thus, in FIG. 5 , anuppermost portion of the epitaxial pillar 114 flares outward relative tolower or intermediate portions of the epitaxial pillar 114 to cover therounded upper surfaces 140 of the dielectric sidewall structure 132.

As shown in FIG. 6 , in some embodiments, an uppermost surface of thedielectric sidewall structure 132, which can exhibit rounded corners142, can be spaced apart vertically from an uppermost planar surface ofthe low-κ dielectric layer 112. Thus, in some embodiments, the uppermostsurface of the dielectric sidewall structure 132 can have a firstheight, h₁, as measured from the upper surface of the substrate 102; andthe uppermost surface of the low-κ dielectric layer 112 can have asecond height, h₂, as measured from the upper surface of the substrate102, wherein the second height, h₂, is greater than the first height,h₁.

With reference to FIGS. 7-19 , a series of cross-sectional views of someembodiments of a semiconductor device with a dielectric sidewallstructure at various stages of manufacture are provided.

As illustrated by FIG. 7 , a substrate 102 is provided. In someembodiments, the substrate 102 is a bulk silicon substrate made ofmonocrystalline silicon. When the substrate 102 is silicon, thesubstrate 102 can be n-type, p-type, or intrinsic silicon. In otherembodiments, the substrate 102 may be other suitable materials, forexample, a silicon carbide substrate, a sapphire substrate, or asemiconductor-on-insulator (SOI) substrate, which can be doped p-type orn-type, and/or may have, for example, a thickness of between about800-2000 nanometers. In still other embodiments, the substrate 102 caninclude e a binary semiconductor material (e.g., GaAs), tertiarysemiconductor material (e.g., InGaAs), or other semiconductor material.

A well region 104, which has a first conductivity type, is formed in thesubstrate 102 by forming a well mask (not shown), such as an oxide,hardmask, and/or photoresist layer for example, over an upper surface ofthe substrate 102. The well mask leaves a portion of the upper substratesurface, which corresponds to the well region 104, exposed; and coversother portions of the upper substrate surface. With the well mask inplace, ions are implanted into the substrate 102 to form the well region104, or a highly doped layer is formed over the substrate 102 and thendopants are out-diffused from the highly doped layer into the substrate102 to form the well region 104.

An isolation region 106, which can have a second conductivity typeopposite the first conductivity type, is formed in the substrate 102 byforming an isolation mask (not shown), such as an oxide, hardmask,and/or photoresist layer for example, over the upper surface of thesubstrate 102. The isolation mask leaves a portion of the uppersubstrate surface, which corresponds to the isolation region 106,exposed; and covers other portions of the upper substrate surface. Withthe isolation mask in place, ions are implanted into the substrate toform the isolation region 106, or a highly doped layer is formed overthe substrate and then dopants are out-diffused from the highly dopedlayer into the substrate to form the isolation region 106. The isolationregion 106 may be formed prior to the well region, or vice versa,depending on the implementation.

As illustrated by FIG. 8 , a dielectric layer 108, which can act as anRPO layer in some embodiments, is formed over the upper surface of thesubstrate 102; and a silicon nitride layer 110, which can act as an etchstop layer in some embodiments, is formed over the dielectric layer 108.A low-κ dielectric layer 112, such as a USG or fluorosilicate glass(FSG) layer for example, is then formed over the silicon nitride layer110.

As illustrated by FIG. 9 , a pillar mask 902, which can be made ofphotoresist material and/or a hardmask for example, is patterned overthe low-κ dielectric layer 112 by using photolithography techniques. Thepillar mask 902 extends over an upper surface of the low-κ dielectriclayer 112, and includes an opening that leaves a portion of the low-κdielectric layer exposed. With the pillar mask 902 in place, an etch iscarried out to remove the exposed portion of the low-κ dielectric layer112 and corresponding portions of the silicon nitride layer 110. Theetch stops on an upper surface of the dielectric layer 108, therebyforming a first recess 904. In some embodiments, the first recess haswidth of approximately 1 micrometer, a length ranging from 1 micrometerto about 30 micrometers, and a height of approximately 30 micrometers.In some embodiments, the etch carried out in FIG. 9 is a plasma etchthat includes C₄F₄, O₂, and Ar gas species included in a plasma chamber,under an applied power ranging from 1000 watts to 8000 watts, forexample.

As illustrated by FIG. 10 , a conformal dielectric liner 132′ is thenformed over an upper surface and sidewalls of the low-κ dielectric layer112, along sidewalls of the silicon nitride layer 110, and over theupper surface of the dielectric layer 108 to partially fill the firstrecess 904. In some embodiments, the conformal dielectric liner 132′ hasa first thickness, t₁, and the dielectric layer has a second thickness,t₂, wherein the first thickness t₁ is greater than the second thickness,t₂. For example, in some embodiments, the first thickness t₁ can rangefrom 10 angstroms to 2000 angstroms; and the second thickness t₂ can beless than the first thickness t₁. In some embodiments, the conformaldielectric liner 132′ is made of SiO₂, and can be formed by spin-ontechniques, chemical vapor deposition (CVD), physical vapor deposition(PVD), plasma enhanced CVD (PECVD), or other techniques.

As illustrated by FIG. 11 , an anisotropic or vertical etch is carriedout with the conformal dielectric liner 132′ in place to remove portionsof the conformal dielectric liner 132′ from the upper surface of thelow-κ dielectric layer 112 and from the upper surface of the dielectriclayer 108. Thus, this anisotropic or vertical etch etches back theconformal dielectric liner 132′ to leave a portion of the conformaldielectric liner as a dielectric sidewall precursor structure 132″ alongsidewalls of the low-κ dielectric layer 112 and along sidewalls of thesilicon nitride layer 110, and leaves an upper surface region of thedielectric layer 108 exposed. Because of the characteristics of theanisotropic or vertical etch used, the dielectric sidewall precursorstructure 132″ still has a thickness which is at least substantiallyequal to t₁, and which is greater than the remaining thickness (˜t₂) ofthe dielectric layer 108. In some embodiments, the etch carried out inFIG. 11 is a dry etch process carried out for a predetermined time, andthis etch includes C₄F₄, O₂, and Ar gas species included in a plasmachamber, for example.

As illustrated by FIG. 12 , an isotropic or wet etch is then carried outto thin the dielectric sidewall precursor structure (132″ of FIG. 11 )to thickness t₁′ and concurrently remove the exposed upper surfaceregion of the dielectric layer 108. In this way, a dielectric sidewallstructure 132 can be formed, which has sidewalls that are aligned withsidewalls of dielectric layer 108, through which upper surface of wellregion 104 is exposed. In some embodiments, carrying out the isotropicor wet etch corresponds to dipping the substrate into an aqueoussolution of dilute hydrofluoric acid for a predetermined time. Thedielectric sidewall structure 132 can have rounded upper surfaces, whichmay be approximately even with an upper surface of the low-κ dielectriclayer 112 or which may be spaced below the upper surface of the low-κdielectric layer 112. Due to the manner in which the etch is carried outto form the dielectric sidewall structure 132, the exposed upper surfaceof the well region 104 is free of damage at this stage—for example, theupper surface of the well region is a monocrystalline surface regionwith little or no dislocations or fractures. Further, because thedielectric sidewall structure 132 still remains in place over the innersidewall of the silicon nitride layer 110, the recess in FIG. 12 canhave vertical or substantially vertical sidewalls, and the dielectriclayer 108 does not undercut the silicon nitride layer 110 as could occurin some conventional approaches.

In some embodiments of FIG. 12 , the dielectric sidewall precursorstructure (132″ of FIG. 11 ) and dielectric layer 108 have the samedielectric material composition as one another, and thus are etched atequal rates to yield sidewalls that are aligned, planar, and/orsubstantially planar for the resultant etched structure, as shown inFIG. 12 . In other embodiments, the dielectric sidewall precursorstructure (132″ of FIG. 11 ) and dielectric layer 108 can have slightlydifferent etch rates. For example, the dielectric sidewall precursorstructure can have a first etch rate and the dielectric layer 108 canhave a second etch rate that differs from the first etch rate for theisotropic or wet etch. Often in such embodiments, the first etch ratewill be slightly greater than the second etch rate, for example by lessthan thirty percent, such that the dielectric layer 108 does notundercut the silicon nitride layer 110 and the recess formed by the etchwill be wider at its upper portions to facilitate better filling withoutgaps or voids.

As illustrated by FIG. 13 , an epitaxial pillar 114 of Si or SiGematerial is epitaxially grown directly on the undamaged well region 104without voids or gaps. The epitaxial growth process used to form theepitaxial pillar 114 initially uses a first set of epitaxial growthconditions to form a lower epitaxial region that corresponds to ann-type region of monocrystalline germanium or monocrystalline SiGe. Theepitaxial growth conditions are then changed to form an upper epitaxialregion that corresponds to a p-type region of monocrystalline Ge ormonocrystalline SiGe that directly contacts the n-type region at a p-njunction. In other embodiments, rather than the p-type region directlycontacting the n-type region at a p-n junction, the epitaxial growthprocess is used to form an intrinsic region of Ge or an intrinsic regionof SiGe between the p-type region and n-type region, such that a p-i-njunction is formed. In other embodiments, the p-type region can beformed before the n-type region. In embodiments where the dielectricsidewall structure 132 has rounded upper surfaces, the epitaxial pillar114 can be grown to flare out overtop the rounded upper surfaces. Inother embodiments, rather than a Ge or SiGe epitaxial material beinggrown for the epitaxial pillar 114, other materials, such asmonocrystalline silicon, a binary semiconductor material (e.g., GaAs),tertiary semiconductor material (e.g., InGaAs), or other semiconductormaterial can be grown to form the epitaxial pillar 114.

As illustrated by FIG. 14 , chemical mechanical planarization (CMP) canbe optionally performed so the dielectric sidewall structure 132 has aplanar upper surface. This planar upper surface is co-planar with anuppermost surface of the epitaxial pillar 114 and is co-planar with anupper surface of low-κ dielectric layer 112. Although this CMP operationis optional, the subsequent figures are illustrated as continuing fromFIG. 14 , but it will be appreciated that the subsequent figures couldequivalently follow from FIG. 13 (e.g., with upper portions of epitaxialpillar 114 still flaring out over upper surface of dielectric sidewallstructure 132).

As illustrated by FIG. 15 , contact opening mask 1502 is formed, and anetch is carried out to form a contact opening 1504 extending downwardthrough the low-κ dielectric layer 112 to expose an upper surface ofsubstrate 102. An ion implantation process can then be carried out so astream of molecules or charged ions pass through the contact opening toform a highly doped well contact region 118.

As illustrated by FIG. 16 , a conductive material, such as tungsten oraluminum for example, is formed. The conductive material extends overthe low-κ dielectric layer 112 and extends downward into the contactopening 1504 to make contact with the highly doped well contact region118. A CMP operation is then carried out to planarize an upper surfaceof the conductive material to establish a conductive contact 1602, andthen a second low-κ dielectric layer 1604 is formed and via openings1606 are formed in the second low-κ dielectric layer 1604.

As illustrated by FIG. 17 , a conductive material, such as copperaluminum for example, is formed over the second low-κ dielectric layer1604. This conductive material extends over the second low-κ dielectriclayer 1604 and extends downward into the via openings, and is planarizedto form conductive vias 1700 and first and second conductive lines 122,126.

As illustrated by FIG. 18 , a window recess mask 1802 is formed over thestructure, and an etch is carried out to remove portions of the secondlow-κ dielectric layer 1604 and/or conductive lines 122, 126, to form awindow opening 128 that increases the amount of impingent radiation thatreaches the epitaxial pillar 114 during operation.

As illustrated by FIG. 19 , an anti-reflective coating (ARC) 130 isformed over the upper surface of the conductive lines 122, 126 andsecond low-κ dielectric layer 1604. Like the window opening 128, the ARC130 increases the amount of impingent radiation that reaches theepitaxial pillar 114 during operation. In some embodiments, the ARC 130is a silicon nitride layer.

An example method 2000 corresponding to some embodiments of FIGS. 7-19is now described with regard to a flowchart of FIG. 20 . However, itwill be appreciated that the structures disclosed in FIGS. 7-19 are notlimited to the method 2000 of FIG. 20 , but instead may stand alone asstructures independent of the method. Similarly, although the method ofFIG. 20 is described in relation to FIGS. 7-19 it will be appreciatedthat the method is not limited to the structures disclosed in FIGS. 7-19but instead may stand alone independent of the structures disclosed inFIGS. 7-19 . In addition, while the method 2000 described by FIG. 20 isillustrated and described herein as a series of acts or events, it willbe appreciated that the illustrated ordering of such acts or events arenot to be interpreted in a limiting sense. For example, some acts mayoccur in different orders and/or concurrently with other acts or eventsapart from those illustrated and/or described herein. Further, not allillustrated acts may be required to implement one or more aspects orembodiments of the description herein, and one or more of the actsdepicted herein may be carried out in one or more separate acts and/orphases.

At 2002, a substrate, which includes a well region, is received. In someembodiments, act 2002 can correspond, for example, to FIG. 7 .

At 2004, a dielectric layer is formed over an upper surface of thesubstrate and over an upper surface of the well region. In someembodiments, act 2004 can correspond, for example, to FIG. 8 .

At 2006, a silicon nitride layer is formed over the dielectric layer. Insome embodiments, act 2006 can correspond, for example, to FIG. 8 .

At 2008, a low-κ dielectric layer is formed over the silicon nitridelayer. In some embodiments, act 2008 can correspond, for example, toFIG. 8 .

At 2010, a pillar mask is formed and patterned over the low-κ dielectriclayer. In some embodiments, act 2010 can correspond, for example, toFIG. 9 .

At 2012, an etch is carried out with the pillar mask in place to removea portion of the low-κ dielectric layer and a portion of the siliconnitride layer. The etch stops on an upper surface of the dielectriclayer, thereby forming a first recess. In some embodiments, act 2012 cancorrespond, for example, to FIG. 9 .

At 2014, a conformal dielectric liner is formed over an upper surface ofthe low-κ dielectric layer, along sidewalls of the low-κ dielectriclayer, along sidewalls of the silicon nitride layer, and over the uppersurface of the dielectric layer to partially fill the first recess. Insome embodiments, act 2014 can correspond, for example, to FIG. 10 .

At 2016, an etch is carried out with the conformal dielectric liner inplace to remove portions of the conformal dielectric liner from theupper surface of the low-κ dielectric and from the upper surface of thedielectric layer, thereby leaving a portion of the conformal dielectricliner as a dielectric sidewall precursor structure and leaving an uppersurface region of the dielectric layer exposed. In some embodiments, act2016 can correspond, for example, to FIG. 11 .

At 2018, an etch is carried out to thin the dielectric sidewallprecursor structure and concurrently remove the exposed upper surfaceregion of the dielectric layer, thereby forming a second recessterminating at an upper surface of the well region and terminating at adielectric sidewall structure. The dielectric sidewall structure extendsalong sidewalls of the low-κ dielectric layer and along sidewalls of thesilicon nitride layer. In some embodiments, act 2018 can correspond, forexample, to FIG. 12 .

At 2020, a pillar of Si or SiGe material is epitaxially grown in thesecond recess to entirely fill the second recess. In some embodiments,act 2020 can correspond, for example, to FIG. 13 .

FIGS. 21-24 illustrate an alternative embodiment in accordance with someembodiments of the present disclosure.

FIG. 21 corresponds to previously discussed FIG. 9 , wherein a substrate102 is provided. The substrate 102 includes a well region 104, which hasa first conductivity type, and an isolation region 106, which can have asecond conductivity type opposite the first conductivity type. Adielectric layer 108, which can act as an RPO layer in some embodiments,is formed over the upper surface of the substrate 102; and a siliconnitride layer 110, which can act as an etch stop layer in someembodiments, is formed over the dielectric layer 108. A low-κ dielectriclayer 112, such as a USG or fluorosilicate glass (FSG) layer forexample, is then formed over the silicon nitride layer 110. An etch iscarried out with a pillar mask 902 in place to remove the exposedportion of the low-κ dielectric layer 112 and corresponding portions ofthe silicon nitride layer 110. The etch stops on an upper surface of thedielectric layer 108, thereby forming a first recess 904.

As illustrated by FIG. 22 , a conformal dielectric liner 132′ is thenformed over an upper surface and sidewalls of the low-κ dielectric layer112, along sidewalls of the silicon nitride layer 110, and over theupper surface of the dielectric layer 108 to partially fill the firstrecess 904. In some embodiments, the conformal dielectric liner 132′ hasa first thickness, t₁, and the dielectric layer has a second thickness,t₂, wherein the first thickness t₁ is greater than the second thickness,t₂.

As illustrated in FIG. 23 , an etch, such as a chemical dry etch (CDE)is carried out for a predetermined time to vertically etch the conformaldielectric liner 132′ and in situ also remove the underlying portions ofthe dielectric layer 108 which are exposed as the etch removes thelateral portions of the conformal dielectric liner 132′. Notably, incontrast to FIGS. 11-12 (where FIG. 11 employed an anisotropic etch andFIG. 12 employed a separate wet etch), the etch in FIG. 23 is a singlein situ etch used to form the dielectric sidewall structure 132. In someembodiments, this in situ etch can be carried out for a predeterminedtime during which the plasma chamber includes C₄F₄, O₂, and Ar gasspecies, for example.

As illustrated in FIG. 24 , an epitaxial pillar 114 of Ge or SiGematerial is epitaxially grown directly on the well region 104 withoutvoids or gaps, similar to as previously discussed with regards to FIG.13 . After FIG. 24 , the manufacturing process can continue asillustrated and described with regards to FIGS. 14-20 to completemanufacturing of the device.

An example method 2500 corresponding to some embodiments employing FIGS.21-24 is now described with regard to a flowchart of FIG. 25 . Asmentioned above, this method can also make use of some embodimentspreviously described with regards to FIGS. 7-19 .

At 2502, a substrate, which includes a well region, is received. In someembodiments, act 2502 can correspond, for example, to FIG. 7 .

At 2504, a dielectric layer is formed over an upper surface of thesubstrate and over an upper surface of the well region. In someembodiments, act 2504 can correspond, for example, to FIG. 8 .

At 2506, a silicon nitride layer is formed over the dielectric layer. Insome embodiments, act 2506 can correspond, for example, to FIG. 8 .

At 2508, a low-κ dielectric layer is formed over the silicon nitridelayer. In some embodiments, act 2508 can correspond, for example, toFIG. 8 .

At 2510, a pillar mask is formed and patterned over the low-κ dielectriclayer. In some embodiments, act 2510 can correspond, for example, toFIG. 21 .

At 2512, an etch is carried out with the pillar mask in place to removea portion of the low-κ dielectric layer and a portion of the siliconnitride layer. The etch stops on an upper surface of the dielectriclayer, thereby forming a first recess. In some embodiments, act 2512 cancorrespond, for example, to FIG. 21 .

At 2514, a conformal dielectric liner is formed over an upper surface ofthe low-κ dielectric layer, along sidewalls of the low-κ dielectriclayer, along sidewalls of the silicon nitride layer, and over the uppersurface of the dielectric layer to partially fill the first recess. Insome embodiments, act 2514 can correspond, for example, to FIG. 22 .

At 2516, an etch is carried out with the conformal dielectric liner inplace to remove portions of the conformal dielectric liner from theupper surface of the low-κ dielectric while leaving portions of theconformal dielectric liner along sidewalls of the low-κ dielectric andsilicon nitride layer. In 2516, the etch also removes underlyingportions of the dielectric layer to expose an upper surface of thesubstrate. In some embodiments, act 2516 can correspond, for example, toFIG. 23 .

At 2518, a pillar of Si or SiGe material is epitaxially grown on theexposed upper surface of the substrate. In some embodiments, act 2518can correspond, for example, to FIG. 24 .

In some embodiments, the present disclosure relates to an integratedcircuit (IC) disposed on a silicon substrate, which includes a wellregion having a first conductivity type. A dielectric layer is arrangedover an upper surface of the silicon substrate, and extends over outeredges of the well region and includes an opening that leaves an innerportion of the well region exposed. An epitaxial pillar of SiGe or Geextends upward from the inner portion of the well region. The epitaxialpillar includes a lower epitaxial region having the first conductivitytype and an upper epitaxial region having a second conductivity type,which is opposite the first conductivity type. A dielectric sidewallstructure surrounds the epitaxial pillar and has a bottom surface thatrests on an upper surface of the dielectric layer.

Other embodiments relate to a method. In this method, a substrate, whichincludes a well region, is received. A dielectric layer is formed overan upper surface of the substrate and over an upper surface of the wellregion. A silicon nitride layer is formed over the dielectric layer, anda low-κ dielectric layer is formed over the silicon nitride layer. Aportion of the low-κ dielectric layer and an underlying portion of thesilicon nitride layer are selectively removed to form a first recessthat exposes an upper surface of the dielectric layer. A conformaldielectric liner is formed over an upper surface of the low-κ dielectriclayer, along sidewalls of the low-κ dielectric layer, along sidewalls ofthe silicon nitride layer, and over the exposed upper surface of thedielectric layer to partially fill the first recess. A first etch iscarried out with the conformal dielectric liner in place to removeportions of the conformal dielectric liner from the upper surface of thelow-κ dielectric layer and from the upper surface of the dielectriclayer, thereby leaving a portion of the conformal dielectric liner as adielectric sidewall precursor structure along sidewalls of the low-κdielectric layer and along sidewalls of the dielectric layer and whileleaving an upper surface region of the dielectric layer exposed.

Still other embodiments relate to an integrated circuit (IC). The ICincludes a silicon substrate including a well region having a firstconductivity type. A dielectric layer is arranged over an upper surfaceof the silicon substrate. The dielectric layer extends over outer edgesof the well region and includes a first opening that leaves an innerportion of the well region exposed. A silicon nitride layer is arrangedover the dielectric layer and includes a second opening which is alignedwith the first opening and which leaves the inner portion of the wellregion exposed. A low-κ dielectric layer is arranged over the siliconnitride layer and includes a third opening which is aligned with thefirst opening and the second opening and which leaves the inner portionof the well region exposed. An epitaxial pillar of SiGe or Ge extendsupward from the inner portion of the well region to an upper region ofthe low-κ dielectric layer. The epitaxial pillar includes a lowerepitaxial region having the first conductivity type and an upperepitaxial region having a second conductivity type, which is oppositethe first conductivity type. A dielectric sidewall structure surroundsthe epitaxial pillar. The dielectric sidewall structure has a bottomsurface that rests on an upper surface of the dielectric layer and hasan upper surface proximate to the upper region of the low-κ dielectriclayer.

Still other embodiments relate to a method. In this method, a substrateis received. A first dielectric layer is formed over an upper surface ofthe substrate, and a second dielectric layer is formed over the firstdielectric layer. A portion of the second dielectric layer isselectively removed to form a first recess that exposes an upper surfaceof the first dielectric layer. A conformal dielectric liner is formedover an upper surface and along sidewalls of the second dielectriclayer, and over the exposed upper surface of the first dielectric layerto partially fill the first recess. A first etch is carried out toremove lateral portions of the conformal dielectric liner, therebyleaving a remaining portion of the conformal dielectric liner as adielectric sidewall precursor structure along sidewalls of the seconddielectric layer while leaving an upper surface region of the firstdielectric layer exposed. A thickness of the dielectric sidewallprecursor structure as measured from an innermost sidewall of thedielectric sidewall precursor to a nearest sidewall of the seconddielectric layer is greater than a thickness of the first dielectriclayer as measured from an upper surface of the first dielectric layer toan upper surface of the substrate. A second etch, which has a differentetching character than the first etch, is carried out to thin thedielectric sidewall precursor structure and concurrently remove theexposed upper surface region of the first dielectric layer, therebyforming a second recess terminating at an upper surface of thesubstrate. A pillar of semiconductor material is formed in the secondrecess.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An integrated circuit (IC), comprising: asubstrate including a well region; an epitaxial pillar extending upwardfrom the well region, the epitaxial pillar including a lower epitaxialregion having a first conductivity type and an upper epitaxial regionhaving a second conductivity type, which is opposite the firstconductivity type; a dielectric layer arranged over an upper surface ofthe substrate and having inner sidewalls that contact outer sidewalls ofthe lower epitaxial region, such that the dielectric layer extends overouter edges of the well region; and a dielectric sidewall structurehaving a bottom surface that rests on an upper surface of the dielectriclayer and having an inner sidewall that contacts outer sidewalls of theupper epitaxial region and outer sidewalls of the epitaxial pillarbeneath the upper epitaxial region.
 2. The IC of claim 1, wherein thedielectric layer and dielectric sidewall structure have the samedielectric material composition as one another.
 3. The IC of claim 1,wherein the dielectric layer has a first etch rate and the dielectricsidewall structure has a second etch rate that differs from the firstetch rate for a predetermined etch, and wherein the first etch rate isbetween 70% and 130% of the second etch rate.
 4. The IC of claim 1,wherein the upper epitaxial region and the lower epitaxial regioncorrespond to a photodiode configured to absorb incident radiation, theIC further comprising: an aluminum copper layer disposed over thesubstrate, wherein the aluminum copper layer includes an opening alignedover an upper surface of the epitaxial pillar and through which theincident radiation may pass through the aluminum copper layer to thephotodiode; and an anti-reflective coating disposed over the aluminumcopper layer and lining the opening of the aluminum copper layer.
 5. TheIC of claim 1, wherein the epitaxial pillar further comprises anintrinsic region of Si or SiGe separating the lower epitaxial regionfrom the upper epitaxial region.
 6. The IC of claim 5, wherein the innersidewalls of the dielectric sidewall structure contact outer sidewallsof the intrinsic region.
 7. An integrated circuit (IC), comprising: asubstrate including a well region; a dielectric layer arranged over anupper surface of the substrate, the dielectric layer extending overouter edges of the well region and including an opening that leaves aninner portion of the well region exposed; an epitaxial pillar of SiGe orGe extending upward from the inner portion of the well region; adielectric sidewall structure surrounding the epitaxial pillar andhaving a bottom surface that rests on an upper surface of the dielectriclayer; a silicon nitride layer disposed over the dielectric layer,separated from the epitaxial pillar by the dielectric sidewallstructure; and a low-k dielectric layer arranged over an upper surfaceof silicon nitride layer, the low-k dielectric layer extending to anupper surface of the epitaxial pillar.
 8. The IC of claim 7, wherein thelow-k dielectric layer has inner sidewalls that are aligned with innersidewalls of the silicon nitride layer.
 9. The IC of claim 7, wherein anouter sidewall of the dielectric sidewall structure contacts an innersidewall of the silicon nitride layer.
 10. The IC of claim 7, whereinthe epitaxial pillar comprises a lower epitaxial region with a firstconductivity type and an intrinsic region over the lower epitaxialregion, and wherein the dielectric layer contacts the lower epitaxialregion.
 11. The IC of claim 10, wherein a lowermost portion of theintrinsic region has a first height measured from an upper surface ofthe substrate, and wherein a lowermost portion of the silicon nitridelayer has a second height that is greater than the first height.
 12. TheIC of claim 10, wherein the dielectric layer contacts the intrinsicregion.
 13. An integrated circuit (IC), comprising: a substrateincluding a well region; an epitaxial pillar extending upward from thewell region, the epitaxial pillar including a lower epitaxial regionhaving a first conductivity type and an upper epitaxial region having asecond conductivity type, which is opposite the first conductivity type;a dielectric layer arranged over an upper surface of the substrate andhaving inner sidewalls that contact outer sidewalls of the lowerepitaxial region, such that the dielectric layer extends over outeredges of the well region; a dielectric sidewall structure having abottom surface that rests on an upper surface of the dielectric layerand bordering outer sidewalls of the epitaxial pillar; and a low-kdielectric layer bordering outer sidewalls of the dielectric sidewallstructure and extending from beneath the upper epitaxial region to anupper surface of the epitaxial pillar.
 14. The IC of claim 13, whereininner sidewalls of the dielectric sidewall structure have rounded uppersurfaces, and where an upper surface of the epitaxial pillar flaresoutward over the rounded upper surfaces.
 15. The IC of claim 14, whereinthe low-k dielectric layer contacts the inner sidewalls of the epitaxialpillar.
 16. The IC of claim 13, wherein the epitaxial pillar furthercomprises an intrinsic region of Si or SiGe separating the lowerepitaxial region from the upper epitaxial region.
 17. The IC of claim16, wherein intrinsic region is level with a bottom surface of the low-kdielectric layer.
 18. The IC of claim 13, wherein the bottom surface ofthe dielectric sidewall structure extends beneath the bottom surface ofthe low-k dielectric layer.
 19. The IC of claim 13, wherein a lowermostportion of the low-k dielectric layer has a first height measured froman upper surface of the substrate, and wherein an uppermost portion ofthe lower epitaxial region has a second height that is less than thefirst height.
 20. The IC of claim 13, wherein inner sidewalls of thedielectric layer are aligned with inner sidewalls of the dielectricsidewall structure such that outer sidewalls of the epitaxial pillarcontinuously extend from a lower surface of the dielectric layer to anupper surface of the dielectric sidewall layer.